threeeye
bc1d038eac
Squashed backup commit (no shallow-clone history issues) of xiaomi-mt6833-dev/kernel_xiaomi_mt6833 (lineage-23.2 branch, upstream commit 9eece662e) plus all fixes applied to get everpal_defconfig building clean against a modern (GCC 15.2.0) toolchain -- see the previous commit message on the lineage-23.2 branch (also in this repo history is not available here since this is a squashed snapshot; full incremental history lives in the local DL380 checkout and the upstream GitHub remote). Upstream: https://github.com/xiaomi-mt6833-dev/kernel_xiaomi_mt6833 (lineage-23.2)
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1.9 KiB
ReStructuredText
57 lines
1.9 KiB
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.. -*- coding: utf-8; mode: rst -*-
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.. _touch:
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*************
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Touch Devices
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*************
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Touch devices are accessed through character device special files named
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``/dev/v4l-touch0`` to ``/dev/v4l-touch255`` with major number 81 and
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dynamically allocated minor numbers 0 to 255.
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Overview
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========
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Sensors may be Optical, or Projected Capacitive touch (PCT).
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Processing is required to analyse the raw data and produce input events. In
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some systems, this may be performed on the ASIC and the raw data is purely a
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side-channel for diagnostics or tuning. In other systems, the ASIC is a simple
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analogue front end device which delivers touch data at high rate, and any touch
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processing must be done on the host.
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For capacitive touch sensing, the touchscreen is composed of an array of
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horizontal and vertical conductors (alternatively called rows/columns, X/Y
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lines, or tx/rx). Mutual Capacitance measured is at the nodes where the
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conductors cross. Alternatively, Self Capacitance measures the signal from each
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column and row independently.
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A touch input may be determined by comparing the raw capacitance measurement to
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a no-touch reference (or "baseline") measurement:
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Delta = Raw - Reference
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The reference measurement takes account of variations in the capacitance across
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the touch sensor matrix, for example manufacturing irregularities,
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environmental or edge effects.
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Querying Capabilities
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=====================
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Devices supporting the touch interface set the ``V4L2_CAP_VIDEO_CAPTURE`` flag
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and the ``V4L2_CAP_TOUCH`` flag in the ``capabilities`` field of
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:c:type:`v4l2_capability` returned by the
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:ref:`VIDIOC_QUERYCAP` ioctl.
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At least one of the read/write or streaming I/O methods must be
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supported.
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The formats supported by touch devices are documented in
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:ref:`Touch Formats <tch-formats>`.
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Data Format Negotiation
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=======================
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A touch device may support any I/O method.
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